Method and apparatus for locating the surface of a liquid metal bath

ABSTRACT

A method and apparatus for locating the surface of a liquid metal bath, particularly intended for use with a basic oxygen steelmaking furnace or an open hearth in which oxygen is used. Oxygen is introduced to such furnaces with a lance which is lowered by a cable and drum to start a blowing operation. The invention measures the apparent weight of the lance as it is lowered. When the lance first contacts the bath, the bath exerts a momentary buoyant effect thereon. The resulting change in the apparent weight of the lance is detected. A memory device remembers the position of the lance when it makes contact, and this position is displayed on a recorder.

United States Patent 1 De Bray I. I

[ 51 Jan. 2, 1973 541 METHOD AND APPARATUS FOR LOCATING THE SURFACE OF Av LIQUID METAL BATH A [75] Inventor: Harold W. De Bray, MonroevilleBorough, Pa.

[73] Assignee: United States Steel Corporation,

Pittsburgh, Pa.

22 Filed: Jan. 28, 1971 [21] Appl. N0.: 110,496

[52} U.S.Clt ..2 66/34LM, 75/60 [51] Int. Cl ..C2lc 7/00 [58] Field ofSearch ..75/59, 60; 266/34 L, 34 LM, 266/35; 33/1266, 126.7 A

[56] References Cited UNITED STATES PATENTS 3,540,879 11/1970 Carlson....75/60 3,140,609

7/1964 Mayes ..33/l26.6

3,128,557 4/1964 Childs 33/1266 3,372,023 3/1968 Kraineretal ..75/60Primary Examiner-Gerald A. Dost Attorney-Walter P. Wood ABSTRACT Amethod and apparatus for locating the surface of a liquid metal bath,particularly intended for use with a basic oxygen steelmaking furnace oran open hearth in which oxygen is used. Oxygen is introduced to suchfurnaces with a lance which is lowered by a cable and drum to start ablowing operation. The invention measures the apparent weight of thelance as it is lowered. When the lance first contacts the bath, the bathexerts a momentary buoyant effect thereon. The resulting change in theapparent weight of the lance is detected. A memory device remembers theposition of the lance when it makes contact, and this position isdisplayed on a recorder.

10 Claims, 4 Drawing Figures POSITION TRANSMITTER COMPUTER ZPEN RECORDER,PATENTEDJAK 2197s SHEET 1 UF 2 POSITION TRANSMITTER RECORDER LOGICCOMPUTER Z PEN RECORDER 'nwewran 0 H. DE BRA) a/HJZ his Alforna'y I'M R0AIENTEDM 191's 3.708.159 A SHEET 2 OF 2 22 F T r hrs-L 3 RED LINE EEWL/IVE INVENTOR HAROLD m 05 any [MM Z v his Alla/00y METHOD AND APPARATUSFGR LOCATING TI-IE water-cooled lances which extend into the furnacefrom above. Conventionally the lance is suspended from a hoist, which atthe start of a blowing operation lowers the lance into the furnace. Itis important that the operator position the lance tip in proper relationto the bath surface. In an oxygen furnace the lance tip commonly ispositioned several inches above the bath surface, while in an openhearth it is usually positioned at the surface or a little below. Animproperly positioned lance not only leads to waste of oxygen and a lessefficient steelmaking process, but may contribute to atmosphericpollution. The operator has difficulty in determining the exact locationof the bath surface, which is wholly obscured in an oxygen furnace andextremely hard to observe in an open hearth.

An object of my invention is to provide an improved method and apparatusfor locating the surface of a bath, to which gas is introduced through alance, wherein the criterion for locating the surface is the momentaryloss of weight in the lance as the lance contacts the bath.

A further object is to provide a method and apparatus for locating thebath surface in which I continuously measure the distance the lancetravels as it is introduced to a vessel and transfer this measurement ofposition to memory at the exact time that a momentary V The lance isalsoequipped with a safety chain 19 which I supports it with the tip outof contact with the furnace and the pen of which continuously traces aline 22' representative of the weight on a chart 23. In actual practiceI may dispense with this recorder, but I have shown it to facilitate theexplanation of my invention.

FIG. 2 illustrates a typical chart 23. obtained with recorder21. Thechart travels downwardly in the recorder; hence the lower end of line 22represents the weight when the operator begins to lower the lance.Whenever the weight drops or increases, the line moves to the left orright respectively. The first segment 22a of the line is vertical exceptfor minor disturbances. When the lance tip first contacts the metalM,the metal exerts a buoyant effect on the lance and there is a suddendrop in its apparent weight. This weight is only momenweight lossisdetected. The output of the memory is FIG. I is adiagrammatic view of abasic oxygen steelmaking furnace and lance equipped with my apparatusfor locating the bath surface in the furnace;

FIG. 2 is a recorder plot of the lance weight as the lance is loweredinto a furnace as shown in FIG. 1;

FIG. 3 is a recorder plot obtained with my preferred apparatus embodyinga computer or special purpose logic system for detecting momentaryweight loss in the lance; and I FIG. 4 is a block diagram illustratingmy preferred arrangement of modules in the computer or logic system.

FIG. 1 shows diagrammatically a conventional basic oxygen furnace 10,which contains a bath of liquid ferrous metal M and an overlying slaglayer 8. The furnace is equipped with the usual water-cooled lance 12for introducing oxygento the metal, and hood 13 for collectingoff-gases. The lance is suspended from a cable 14, which runs over asheave l5 and winds on a drum 16. A reversible electric motor 17drivesthe drum in either. direction for lowering or raising the lance,An operator controls the motor through a push-button switch 18.

tary, as oxygen discharging from the lance blows the metal aside, asindicated at 24 in FIG. I. This momen-- tary drop shows up as a spike22b in line 22. If the operator continues to lower the lance until thecable 14 is fully unwound from drum 16, the safety chain 19 supports thelance. This shows up as a straight vertical segment 220 near the leftedge of the chart, indicative. of a negligible voltage signal from theload cell 20. When the operator raises the lance to its proper positionfor blowing, the line again becomes essentially vertical, as indicatedat 22d.

the operator observes how much cable 14 has been unwound from drum 16when the recorder pen traces the spike 22b, he knows the exact locationof the bath surface. He can then position the lance 12 any desireddistance above or below this surface. However, it would be extremelydifficult for an operator to make an accurate observation directly, andmy apparatus preferably includes a logic computer 28 to facilitatemaking this observation.-

I mechanically connect a position-transmitter 29 to the cable drum 16.The transmitter developes a voltage signal of a magnitude proportionalto the position of rotation of thedrum and-hence of the lance position.In the illustrated circuit, this signal is'at its maximum value (e .g.10 volts) when cable 14 is fully. wound on the drum and zero when lance12 is at its extreme limit of travel in furnace 10, although I couldreverse this relation. Voltage signals from both the load cell 20 andthe position-transmitter 29 go to the computer 28. The voltage signalfrom the position-transmitter also goes to a two-pen recorder 30, onepen of which traces a line 31 (green line") representative of the lanceposition on a chart 32. As the lance 12 is lowered into the furnace 10,the computer 28detect's the weight drop when the tip contacts the metaland remembers this position. The otherv pen of recorder 30 traces a line33(red line) which jogs when the computer transmits a signal I v to therecorder that the lance tip has madecontact.

two-pen downwardly in therecor'der, and the lower ends of both lines 31and 33 represent conditions before the operator begins to lower thelance l2. Whenever the lance moves downwardly or upwardly, the greenline moves .to the left or right respectively. The first segment 31a ofthe green line is vertical and near the right edge of the chart. Thegreen pen traces this segment while the lance is stationary before thecable starts to unwind. The next segment 31b slopes upwardly toward theleft and is traced as the lance moves downwardly. The first segment 33aof the red line 33 is vertical and near the left edge of the chart. Thered pen traces this segment before the computer signals that the lancetip has made contact. The contact signal shows up as a jog 33b towardthe right in the red line. Thereafter the red line continues verticallyupward, as indicated at 33c. The position of the green line when the jog33b occurs locates the bath surface. Normally the operator discontinueslowering the lance once he observes the jog and raises it away from thebath surface, as indicated by segment 31c of the green line. When thelance is positioned' properly for blowing, the operator stops the lanceas indicated by segment 31d.

FIG. 4 shows in block diagram the preferred arrangement of my electriccircuit, including the essential modules of my computer 28. The voltagesignal from the load cell goes through anamplifier 36 and thence torelays 37 and 38, and to a differentiating module 39 of the computer. Iconnect the output side of module 39 to another relay 40. The voltagesignal from the position-transmitter 29 goes through an amplifier 43 andthence to a relay 44, to a track-andhold" module 45 of the computer, andto the two-pen recorder 30. l connectthe track-and-hold" module to avoltage source through normally closed contacts 370 and 38a and normallyopen contacts 40a and 44a of .the respective relays, and through aone-shot" 46. l connect the output side of module 45 to the two-penrecorder 30.

I set relay 37 so that it is energized whenever the signal from the loadcell 20 indicates a weight below a predetermined maximum, and relay 38sothat it is energized whenever the signal from the load cell in-'dicates a weight above a predetermined minimum. For

' example, if the lance weighs 600 pounds, I may set the level of courseis known. Thus the weight must be within a predetermined range tomaintain contacts 37a and 380 closed and the lance must reach apredetermined position to close contact 440. Unless these contacts areall closed, the computer 28 does not transmit a signal to the two-penrecorder 30. ln this manner I prevent false observations from appearingas a signal that the lance tip has contacted the bath.

The differentiating module 39 continuously determines AW/Ar (weight withrespect to time), but ignores the minor disturbances such as take placein segment 220 on chart 23 (FIG. 2). As long as the weight isessentially constant, this module produces no signal. When the weightdrops sharply as the lance tip reaches the bath surface, the suddenchange induces the module to transmit a measurable signal whichcorresponds with spike 2212. This signal energizes relay 40 whereuponcontact 400 closes. The one-shot" 46 transmits a standardized pulse tothe "track-an'd-hold" memory module 45, provided contacts 37a, 38a and44a are closed. Module 45 now stores in memory and transmits to thetwo-pen recorder 30 the signal which.

produces the jog 33b in the red line 33.

l have not describedin detail the various components I use in myapparatus, since per se they are known commercially available items. Oneexample of a suitable load cell 20 is available from Revere Corporationof America, a subsidiary of Neptune Meter Company, Wallingford,Connecticut, under the designation "USPl-S-A. One example of a suitablerecorder 21 (if included) is available from Esterline Corporation,lndianapolis, Indiana, under the designation Esterline Angus. Oneexample of a suitable position-transmitter 29 is available from HelipotDivision of Beckman lnstru- 'ments, Fullerton, California, under thedesignation Helipot, Model A RSK 1.25. One example of a suitable two-penrecorder 30 is available from Consolidated Electrodynamics, a subsidiaryof Bell and Howell, Bridgeport, Connecticut, under the designation l 8-300 Series Recorder. One Example of a module suitable for use both as adifferentiating module 39 and asa track-and-hoid" module 45 is availablefrom Control; Products Division, Bell and Howell, under the designation19-407 Dynamic Response Module". One example of a suitable one-shot" isavailable from the lastname source under the designation 19-507".

From the foregoing description it is seen that my invention'affords asimple method and readily constructed apparatus for positively locatingthe surface of a liquid metal bath in a vessel where visibility iswholly or partially obscured. As applied to steelmaking furnaces, theinvention enables as oxygen lance to be positionedat a precise distancewith respect to a bath surface. Thusthe invention not only promotesefficiency, but assists in overcoming atmospheric pollution.

v lclairn:

1. In the operation of a process wherein a gas is introduced through alance to a liquid bath, the lance is lowered from above into the vesselwhich contains said bath, and when the lance initially contacts thebath, the buoyant effect of the bath produces a drop in the ap parentweight of the lance, which drop is only momentary as gas from the lanceblows the liquid of the bath 1 aside, an improved method of locating thebath surface comprising continuously measuring the distance throughwhich the lance is lowered, continuously measuring the apparent weightofthe lance as it is lowered,

2. An operation as defined in claim 1 in which said bath is ferrousmetal and the gas is oxygen.

3. An'operation as defined in claim 1 in which the lance position iscontinuously recorded and the ap parent weight drop of the lance isrecorded on the recording of the lance position.

I 4. A method as defined in claim 3 in which the weight drop is measuredthrough a computer;

5. The combination, with a vessel for containing a liquid bath, a lancefor introducing gas to said bath,- and means for suspending said lanceand lowering it into said vessel or raising it therefrom, whereby thebuoyant effect of said bath produces a drop in the apparent weight ofsaid lance when the lance initially contacts the bath, which drop isonly momentary as gas from the lance blows the liquid of the bath aside,of an apparatus for locating the bath surface, said apparatus comprisingmeans connected with said lance-suspending means for measuring theapparent weight of said lance as it is lowered into said vessel, meansconnected with said lance-suspended means for measuring the distancesaid lance, and said firstmamed measuring means includes a 1 load cellconnected with said cable.

7. A combination as defined in claim 5 in which said suspending meansincludes a motor-driven drum and a cable winding on said drum andconnected to said lance, and said second-named measuring means includesa position-transmitter connected with said drum.

8. A combination as defined in claim 5 in which the means fordetermining the distance the lance has traveled when its weight dropsincludes a computer connected with said first-named measuring means fortransmitting a signal that a'drop in weight has occurred,

and a recorder connected to said second-named mea-' suring means and tosaid computer.

9. A combination as defined in claim 8 in which said computer includesmeans for preventing transmissionof signals unless the lance weight iswithin a predetermined range and the lance position is within apredetermined distance of the bath surface.

10. A combination as defined in claim 5 in whichsaid suspending meansincludes a motor-driven drum and a cable winding on said drum andconnected with said lance, said first-named measuring means includes aload cell connected with said cable, said second-named measuring meansincludes a position-transmitter connected with said drum, and means fordetermining the distance the lance has traveled when its weight dropsincludes a computer connected with said load cell and Ya recorderconnected with said position-transmitter and with said computer.

1. In the operation of a process wherein a gas is introduced through alance to a liquid bath, the lance is lowered from above into the vesselwhich contains said bath, and when the lance initially contacts thebath, the buoyant effect of the bath produces a drop in the apparentweight of the lance, which drop is only momentary as gas from the lanceblows the liquid of the bath aside, an improved method of locating thebath surface comprising continuously measuring the distance throughwhich the lance is lowered, continuously measuring the apparent weightof the lance as it is lowered, detecting the momentary drop in theapparent weight, and recording the lance position at the point at whichsaid drop occurs.
 2. An operation as defined in claim 1 in which saidbath is ferrous metal and the gas is oxygen.
 3. An operation as definedin claim 1 in which the lance position is continuously recorded and theapparent weight drop of the lance is recorded on the recording of thelance position.
 4. A method as defined in claim 3 in which the weightdrop is measured through a computer.
 5. The combination, with a vesselfor containing a liquid bath, a lance for introducing gas to said bath,and means for suspending said lance and lowering it into said vessel orraising it therefrom, whereby the buoyant effect of said bath produces adrop in the apparent weight of said lance when the lance initiallycontacts the bath, which drop is only momentary as gas from the lanceblows the liquid of the bath aside, of an apparatus for locating thebath surface, said apparatus comprising means connected with saidlance-suspending means for measuring the apparent weight of said lanceas it is lowered into said vessel, means connected with saidlance-suspended means for measuring the distance said lance travels asit is lowered into said vessel, and means connected with tHe twomeasuring means for detecting the momentary drop in apparent weight anddetermining the distance said lance has traveled when said drop occurs.6. A combination as defined in claim 5 in which said suspending meansincludes a motor-driven drum and a cable winding on said drum andconnected to said lance, and said first-named measuring means includes aload cell connected with said cable.
 7. A combination as defined inclaim 5 in which said suspending means includes a motor-driven drum anda cable winding on said drum and connected to said lance, and saidsecond-named measuring means includes a position-transmitter connectedwith said drum.
 8. A combination as defined in claim 5 in which themeans for determining the distance the lance has traveled when itsweight drops includes a computer connected with said first-namedmeasuring means for transmitting a signal that a drop in weight hasoccurred, and a recorder connected to said second-named measuring meansand to said computer.
 9. A combination as defined in claim 8 in whichsaid computer includes means for preventing transmission of signalsunless the lance weight is within a predetermined range and the lanceposition is within a predetermined distance of the bath surface.
 10. Acombination as defined in claim 5 in which said suspending meansincludes a motor-driven drum and a cable winding on said drum andconnected with said lance, said first-named measuring means includes aload cell connected with said cable, said second-named measuring meansincludes a position-transmitter connected with said drum, and means fordetermining the distance the lance has traveled when its weight dropsincludes a computer connected with said load cell and a recorderconnected with said position-transmitter and with said computer.